1. Field of the Invention
Apparatus and methods consistent with the present invention relate to a diode circuit having a passive element property, and an impedance modulator and a direct current (DC) source that use the diode circuit, and more particularly, to a diode circuit that has a passive element property by connecting a DC path to a diode and circulating a DC current, and an impedance modulator and a DC source that use the diode circuit.
2. Description of the Related Art
Various elements of an electronic circuit are classified into active elements or passive elements according to their characteristics. The passive elements consume energy while the active elements supply energy. Resistors, inductors, capacitors, and the like correspond to the passive elements. Diodes, transistors, and the like are some examples of the active elements.
FIGS. 1A and 1B are views illustrating a current property of a diode to which a predetermined radio frequency (RF) signal, i.e., an alternating current (AC) power vD(t), is applied. More specifically, if vD(t)=V0 cos ωt is applied, a current iD(t) flowing through the diode is expressed as in Equation 1:
                                          i            D                    ⁡                      (            t            )                          =                                            I              S                        ⁢                          ⅇ                                                                    v                    D                                    ⁡                                      (                    t                    )                                                                    nV                  T                                                              =                                                    I                S                            ⁢                              ⅇ                                                                            V                      0                                        ⁢                    cos                    ⁢                                                                                  ⁢                    ω                    ⁢                                                                                  ⁢                    t                                                        nV                    T                                                                        =                                          I                S                            ⁢                                                ⅇ                                      α                    ⁢                                                                                  ⁢                    cos                    ⁢                                                                                  ⁢                    ω                    ⁢                                                                                  ⁢                    t                                                  ⁡                                  (                                      where                    ,                                          α                      =                                                                        V                          0                                                                          nV                          T                                                                                                      )                                                                                        (        1        )            wherein IS denotes a reverse saturation current, VT denotes a threshold voltage, and n denotes a positive integer including “0”. Equation 1 can also be expressed as in Equation 2:
                                                                                          i                  D                                ⁡                                  (                  t                  )                                            =                            ⁢                                                I                  S                                ⁡                                  (                                                                                    a                        0                                            2                                        +                                                                  a                        1                                            ⁢                      cos                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      t                                        +                                                                  a                        2                                            ⁢                      cos2                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      t                                        +                                                                  a                        3                                            ⁢                      cos                      ⁢                                                                                          ⁢                      3                      ⁢                      ω                      ⁢                                                                                          ⁢                      t                                        +                    …                    +                                                                  a                        n                                            ⁢                      cos                      ⁢                                                                                          ⁢                      n                      ⁢                                                                                          ⁢                      ω                      ⁢                                                                                          ⁢                      t                                                        )                                                                                                        =                            ⁢                                                                    I                    S                                    ⁡                                      (                                                                  a                        0                                            2                                        )                                                  +                                                      I                    S                                    ⁢                                      a                    1                                    ⁢                  cos                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                                      I                    S                                    ⁢                                      a                    2                                    ⁢                  cos                  ⁢                                                                          ⁢                  2                  ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                                      I                    S                                    ⁢                                      a                    3                                    ⁢                  cos                  ⁢                                                                          ⁢                  3                  ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                …                +                                                                                                      ⁢                                                I                  S                                ⁢                                  a                  n                                ⁢                cos                ⁢                                                                  ⁢                n                ⁢                                                                  ⁢                ω                ⁢                                                                  ⁢                t                                                                                        =                            ⁢                                                I                                      D                    ⁢                                                                                  ⁢                    C                                                  +                                  i                  1                                +                                  i                  2                                +                                  i                  3                                +                …                +                                  i                  n                                                                                        (        2        )            
As shown in FIGS. 1A and 1B, when an AC signal is applied to the diode, a predetermined intensity of DC current IDC and different frequencies of AC currents i1, i2, . . . , and in are generated due to the parabolic nature of the diode. Thus, the diode cannot be used in an RF path where a DC current is intercepted by a capacitor or the like, and this imposes limits on circuit design.